Rotor for intensive mixers

ABSTRACT

An improved rotor for use in intensive mixers which reduces leakage of material out of the mixers comprising a substantially cylindrical body having affixed thereto a pair of diagonally disposed spiral lobes, said lobes terminating at the respective ends of the rotor at oppositely opposed end plate sections, the distance between the edges of the lobes adjacent the end face plate sections and the internal wall of the mixing chamber being greater than the distance between the edges of the lobes farthest from the end face plate sections and the internal wall of the mixing chamber.

United States Patent Crixell [45 1 June 27, 1972 [541 ROTOR FORINTENSIVE MIXERS [7 2] Inventor: Arthur R. Crlxell, Texas City, Tex.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Dec. 5, 1969 [21] App]. No.: 882,560

52 US. Cl... .259/104, 18/12 s12 51 1111.01. ..B0lf7/00, 82% 1/10 [58]Field ofSearch ..259/104,6, 21,41, 64, 9,

[56] References Cited UNITED STATES PATENTS 2,559,418 7/1951 Ford..259/l04 2,573,825 11/1951 Banovsky et al. ..259/6 X 3,468,518 9/1969Koch ..259/104X 3,348,816 10/1967 Cox ..259/104)( PrimaryExaminer-Jordan Franklin Assistant Examiner--Geo V. LarkinAttorney-Elizabeth F. Sporar, M. N. Cheairs and Neal E. Willis [57]ABSTRACT An improved rotor for use in intensive mixers which reducesleakage of material out of the mixers comprising a substantiallycylindrical body having afiixed thereto a pair of diagonally disposedspiral lobes, said lobes terminating at the respective ends of the rotorat oppositely opposed end plate sections, the distance between the edgesof the lobes adjacent the end face plate sections and the internal wallof the mixing chamber being greater than the distance between the edgesof the lobes farthest from the end face plate sections and the internalwall of the mixing chamber.

6 Claims, 3 Drawing Figures INVENTOR. Arthur R. C rixell AGENTPATENTEflJunz'l m2 57 ,5

sum 2 UF 2 FIGURE 2 FIGURE 3 jN vENTo Arthur R. Cri

AGENT ROTOR FOR INTENSIVE MIXERS BACKGROUND OF THE INVENTION The presentinvention relates to intensive mixers of the type used to blend andmasticate plastics, rubbers, etc. More particularly, thepresentinvention relates to an improved rotor for use in intensive mixers ofthe type commonly referred to as Banbury mixers.

The commonly known intensive mixers of the type used to masticate andmix plastics and rubbers such as polyethylene, polypropylene,polybutadiene and the like generally comprise a closed mixing chamberformed by two cylinders placedside by side with their long axes in aparallel-horizontal relationship, the cylinders communicatingwith eachother at their adjacent outer peripheral portions resulting in a chamberhaving a substantially figure-eight cross-sectional area. In each sideor "loop" of the chamber a mixingmeans or rotor is rotatably mountedparallel and concentrically with the long axis of the cylinder, each ofthe rotors having a pair of generally spiral lobes positioned diagonallyto one another across the long axis of the rotor, the edges of the lobesapproaching close to the internal walls of the mixing chamber so as toimpart shearing to thematerial being processed. The chamber formed bythe two communicating cylinders is closed 'on the respective ends withsuitable end plates through which the rotor shafts extend, the shafts inturn being connected to a suitable drive mechanism located externally ofthe chamber.

In the processing of plastics and rubbers using mixers such as describedabove, shear pressures may become very great within the chamber. Theserather large pressures coupled with a temperature rise which causes theplastic or rubber to flow easily result in thepolymer, rubber, etc.,being forced out of the chamber through any openings which exist. Moregenerally, the materialis forced out at the ends of the chamber nearwhere the rotor shrouds abutthe end plates of the chamberl'lhis leakageof material out of the mixing chamber notonly results in a loss ofproduct but more significantly leads to considerable downtime of themixer due to the fact that the material will accumulate on the rotorseals, shaft and bearings forcing shutdown and repair.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved intensive mixer.

It is a further object of the present invention to provide an intensivemixer having an improved rotor.

Yet another object of the present invention is to provide an improvedrotor for use in intensive mixers which is as effective as prior artrotors in imparting mixing and shearing to materials but which reducesthe leakage of the materials being mixed out of the mixing chamber.

These and other objects of the present invention whichwill becomeapparent from the drawings, the description given hereinand the appendedclaims areachieved by an improvement in an intensive mixer of the typehaving a stationary mixing chamber, said chamber having a substantiallyfigure-eightr shaped crosssectional area, mixing means rotatably mountedin each half of said chamber to impart mixing and shearing of materialcontained therein wherein said mixing means comprises a substantiallycylindrical rotor having a pair of substantially spiral lobes locateddiagonally from one another across the long axis of said rotor, saidrotor having an end face plate section on each end abutting theendsofsaid chamber, the lobes terminating at said end face plate sections, thedistance between the internal wall of said chamber and the edges of thelobes nearest the end face plate sections being greater than thedistance between the internal wall of said chamber and the edges of thelobes locatedfarthest from said end face plate sections, the distancebetween said internal wall of said chamber and the edges of said endface plate sections being substantially equal to the distance betweensaid internal wall and said edges of said lobes located farthest fromsaid end face plate sections.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified diagram partlyin section of a typical intensive mixer.

FIG. 2 is a view partly in section of a conventional rotor mounted inthe mixing chamber of an intensive mixer such as that shown in FIG. 1.

FIG. 3 is a view partly in section of one embodiment of the improvedrotor of the present invention mounted in the mixing chamber of anintensive mixer such as that shown in FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS material. The material to beprocessed is fed into chamber ll through hopper door 14 whence it fallsinto chamber 1 1 and is maintained therein by means of weighted door 15,the mechanisms to control weighted door 15 and hopperdoor 14 beingcontained within housing 16. When the material has been adequatelymixed, it is dropped from the bottom of the chamber through a suitablepneumatically or hydraulically actuated sliding door (not shown).

. Reference is now made to FIG. 2 for a description of a typical rotor,such as rotors 12 and 13 shown in FIG. 1, which is conventionally usedin intensive mixers. of the type commonly referred to as Banbury mixers.For ease of illustration and understanding, only one-half of the mixingchambercontaining one rotor is shown. Rotor 17, which is basicallycomprised of a cylindrical central body having a pair of substantiallyspiral lobes 22 andl23 disposed diagonally'from one another across thelong axis of the central body, is mounted within chamber 18 formed bywalls 19 and end plates 20 and 21. .As is well known by those familiarwith intensive mixers, the edges of lobes 22 and 23 approachclosely totheinside surface of walls 19, the distance from the inside surface ofthe walls to the edges of the lobes being substantially constant at allpoints along the length of the lobe edges: Lobes'22 and 23 terminate ateach end of rotor 17 at a pair of oppositely disposed end face platesections 24 and25. Bearings, 26 and,27 located at each end of chamber 18serve to rotatably hold rotor 17 in the chamber housing and a suitablepower source (notshown).is connected to shaft 28 of rotor .17 to impartrotation thereto. As is evident, due to the close tolerances between theedges of lobes 22 and 23 and the inside surface of walls 19 of themixing chamber, material which is being mixed in chamber 18 is caused toundergo relatively intense shearing action as it is moved in asubstantially figure-eight pattern within chamber 18. This intenseshearing action, which leads torather large pressure buildups withinchamber 18, coupled -.with the consequent rise in temperatureexperienced by the-material being mixed, results in the material beingquite fluid: Under these conditions, the material readily leaks throughany available openings which usually are'clearances 29; and 31' formedwhere chamberwall l9,end plates 20 and2l, end face plates 24 and 25 andbearings 26 andy27 come together to effect a seal of chamber 18. Asexplained a'bove, this leakage of material out of chamber 18 can resultindamage to the rotor seals and bearings with resultant losses ofproductivity of the system.

Reference is now made to FIG. 3 to show theimproved rotor of thepresentinvention. As can beseen, the rotor of FIG. 3 is substantiallythe sameas that shown inFIGqZtwith the exception that lobes22 and 23contain a notched portion 30 adjacent where lobes 22 and 23terrninateatend faceplate sections 24 and 25. As a result of notchy30,the clearance between the edges of. lobes 22 and 23 and the insidesurface of walls 19 nearest the point where lobes 22 andf23 adjoinendface plates 24 and 25 is greater than the clearance between the insidesurface of walls 19 and the edges of lobes 22 and 23 located farthestfrom end plate sections 24 and 25. Consequently, the large pressuresurges which occur as the material is being sheared do not develop atthe ends of chamber 18 with the result that there is less tendency formaterial to leak through clearances 29 and 31. While minimizing theleakage of material out of chamber 18, the improved rotor of FIG. 3gives substantially the same mixing and masticating results as areachieved with the conventional rotor shown in H6. 2.

As will be readily recognized by those skilled in the art, notch 30 isonly one way to achieve the improved rotor described herein. All that isnecessary is that the lobes be of a design such that the distancebetween the internal wall of the mixing chamber and the edges of thelobes nearest the end plate sections be greater than the distancebetween the internal wall of the chamber and the edges of the lobesfarthest from the end plate sections. This can be achieved in severaldifferent ways, a notch being easiest to accomplish on rotors inexisting equipment. The notch need not be of any particular shape butcan-be rectangular or have a curved surface. Whatever the shape of thenotch, it has been found preferable that it have a length of from topercent of the total length of the edge of the lobe into which it is cutand a depth of at least 2 percent of the perpendicular distance from theedge of the lobe in which it is cut to the center of the cylindricalportion of the rotor. This perpendicular distance is referred to as themajor radius of the rotor, the radius of the cylindrical portion per sebeing referred to as the minor radius. Obviously, the notch can have amaximum depth equal to the difference between the length of the majorradius and length of the minor radius.

The improved rotor of the present invention also encompasses a rotorwherein each of the lobes is continuously tapered from the pointfarthest from the end plate sections to the ends of the lobesterminating at those sections. As can be seen, this tapering can be suchthat the distance between the internal wall of the chamber and the edgesof the lobes located nearest the end plate sections is substantiallyequal to the perpendicular distance from the edges of the lobes locatedfarthest from the end plate sections to the cylindrical surface of therotor. Also, depending on the mixing pattern desired within the chamber,the continuous tapering can be uniform or non-uniform such that a planarprojection of the lobe would appear as a portion of a circle, forexample, in the case of uniform tapering, or a portion of a parabola,ellipse or the like in the case of non-uniform tapering. The particularchoice of tapering will depend on the material being mixed and thedesired mixing action.

While not absolutely necessary, it is preferable that the lobes on therotors be of unequal length. This contributes to the overall mixingability of the rotor and insures a more homogeneous product. As is wellknown, both the chamber housing and the rotors can be cored whereby thechamber and rotors can be heated or cooled by the use of suitableheattransfer mediums. The rotor finds particular utility in intensivemixers of the batch type commonly referred to as Banbury mixers. a

What is claimed is:

1. In an intensive mixer of the type having a stationary mixing chamber,said chamber having a substantially figure-eightshaped cross-sectionalarea, mixing means rotatably mounted in each half of said chamber toimpart mixing and shearing of material contained therein, theimprovement whereby leakage of said material out of said chamber issubstantially reduced wherein said mixing means comprises asubstantially cylindrical rotor having a pair of substantially spirallobes located diagonally from one another across the long axis of saidrotor, said rotor having an end face plate section on each end abuttingthe ends of said chamber, the lobes terminating at said end face platesections, the distance between the internal wall of said chamber and theedges of the lobes nearest the end face plate sections beincg eater thanthe distance between the internal wall of sai c amber and the edges ofthe lobes located farthest from said end face plate sections, thedistance between said internal wall of said chamber and the edges ofsaid end face plate sections being substantially equal to the distancebetween said internal wall and said edges of said lobes located farthestfrom said end face plate sections.

2. The rotor of claim 1 wherein each edge of said lobes has a notchadjacent said end plate section, said notch having a length of from 10to 20 percent of the total length of the edge of the lobe, said notchhaving a depth of at least 2 percent of the perpendicular distance fromthe edge of the lobe to the center of the cylindrical portion of saidrotor.

3. The rotor of claim 1 wherein said lobes are continuously tapered, thedistance between said internal wall of said chamber and the edges ofsaid lobe nearest said end face plate sections being greater than thedistance between the internal wall of said chamber and said edges ofsaid lobes located farthest from said end plate face sections.

4. The rotor of claim 3 wherein said lobes are uniformly tapered.

5. The rotor of claim 3 wherein said distance between said internal wallof said chamber and said edges of said lobes located nearest said endface plate sections is substantially equal to the perpendicular distancefrom the edges of said lobes located farthest from said end face platesections to the cylindrical surface of said rotor.

6. The rotor of claim 1 wherein said lobes of are different length.

1. In an intensive mixer of the type having a stationary mixing chamber,said chamber having a substantially figure-eight-shaped cross-sectionalarea, mixing means rotatably mounted in each half of said chamber toimpart mixing and shearing of material contained therein, theimprovement whereby leakage of said material out of said chamber issubstantially reduced wherein said mixing means comprises asubstantially cylindrical rotor having a pair of substantially spirallobes located diagonally from one another across the long axis of saidrotor, said rotor having an end face plate section on each end abuttingthe ends of said chamber, the lobes terminating at said end face platesections, the distance between the internal wall of said chamber and theedges of the lobes nearest the end face plate sections being greaterthan the distance between the internal wall of said chamber and theedges of the lobes located farthest from said end face plate sections,the distance between said internal wall of said chamber and the edges ofsaid end face plate sections being substantially equal to the distancebetween said internal wall and said edges of said lobes located farthestfrom said end face plate sections.
 2. The rotor of claim 1 wherein eachedge of said lobes has a notch adjacent said end plate section, saidnotch having a length of from 10 to 20 percent of the total length ofthe edge of the lobe, said notch having a depth of at least 2 percent ofthe perpendicular distance from the edge of the lobe to the center ofthe cylindrical portion of said rotor.
 3. The rotor of claim 1 whereinsaid lobes are continuously tapered, the distance between said internalwall of said chamber and the edges of said lobe nearest said end faceplate sections being greater than the distance between the internal wallof said chamber and said edges of said lobes located farthest from saidend plate face sections.
 4. The rotor of claim 3 wherein said lobes areuniformly tapered.
 5. The rotor of claim 3 wherein said distance betweensaid internal wall of said chamber and said edges of said lobes locatednearest said end face plate sections is substantially equal to theperpendicular distance from the edges of said lobes located farthestfrom said end face plate sections to the cylindrical surface of saidrotor.
 6. The rotor of claim 1 wherein said lobes of are differentlength.